Case for watches

ABSTRACT

A CASE FOR WATCHES FORMED FROM A NON-CORROSIVE FERRITE STAINLESS STEEL PREFERABLY AN FE-CR-MO-NB ALLOY OR FE-CR-MO-TI WHEREBY SAID CASE HAS A HIGH RESISTANCE TO CORROSION AND A HIGH PERMEABILITY TO PROTECT THE MOVEMENT OF THE WATCH FROM AN EXTERNAL MAGNETIC FIELD.

June 1971 HIROSHIV HARIGAYA 3,535,009

CASE FOR WATCHES Filed June 4, 1968 BRASS CASE SIAM/LE /8 8 ss ./L b A110) (456 71551. 0435 arms/van 0F MAGNET/C new (0c) United States Patent Ofice 3,585,009 CASE FOR WATCHES Hiroshi Harigaya, Suwa-shi, Japan, assignor to Kabushiki Kaisha Suwa Seikosha, Tokyo, Japan Filed June 4, 1968, Ser. No. 734,285 Claims priority, application Japan, June 8, 1967, 42/ 36,435 Int. Cl. C22c 39/00 US. Cl. 29-183 3 Claims ABSTRACT OF THE DISCLOSURE A case for watches formed from a non-corrosive ferrite stainless steel preferably an Fe-Cr-Mo-Nb alloy or Fe-Cr-Mo-Ti whereby said case has a high resistance to corrosion and a high permeability to protect the movement of the watch from an external magnetic field.

BACKGROUND OF THE INVENTION This invention relates generally to cases for watches, particularly Wristwatches. The hairspring, one of the most important elements in contributing to the accuracy of a watch, is generally formed from a ferromagnetic material which is also generally referred to as a thermocompensating material. Also, the anchor, escapement wheel, etc. are often made of an iron alloy. Since many of the parts which are determinitive of the accuracy of a watch are ferromagnetic, the accuracy of an unshielded watch is substantially diminished by exposure to an external magnetic field. For this reason, it has become common in the art to provide antimagnetic watches by providing a shield screen of high permeability material, such as pure iron, permalloy, etc. between the case and the movement to protect the latter from the influences of an external magnetic field. However, watches provided with such antimagnetic shielding have a more complicated structure and are therefore more difficult to manufacture and assemble. Further, such watches are heavier in weight and larger in size than an ordinary watch, and accordingly present a less desirable appearance. The materials now used in antimagnetic shields are unsuitable as an outer case due to their inability to resist corrosion.

SUMMARY OF THE INVENTION Generally speaking, in accordance with the invention, a case for watches is provided formed from a non-corrosive ferrite stainless steel such as Fe-Cr-Mo-Nb alloy or Fe-Cr-Mo-Ti alloy whereby the movement of the watch is protected from external magnetic fields and from corrosion. A case formed according to the invention requires no further surface treatment, nor does it require further internal shielding.

Accordingly, it is an object of this invention to provide a case for watches which is both resistant to corrosion and the effects of an external magnetic field.

Another object of the invention is to provide a case for watches which does not require further internal shielding from external magnetic fields.

A further object of the invention is to provide a case for watches which does not require further surface treatment.

Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.

The invention accordingly comprises an article of manufacture possessing the features, properties and the relation of elements which will be exemplified in the article hereinafter described, and the scope of the invention will be indicated in the claims.

Patented June 15, 1971 BRIEF DESCRIPTION OF THE DRAWING For a fuller understanding of the invention, reference is had to the following description taken in connection with the accompanying drawing, in which:

The drawing shows the variations in the rate of Watches with cases made of various materials when said Watches are placed in a magnetic field.

DESCRIPTION OF PREFERRED EMBODIMENTS According to the invention, the case of a watch is formed from a non-corrosive ferrite stainless steel such as Fe-Cr-Mo-Nb alloy or Fe-Cr-Mo-Ti alloy.

An example of the composition of the alloy for this invention is shown in Table 1 in terms of percentages by weight.

TABLE 1 Cr 19.2 Mo 2.0 C 0.03 Nb 0.31 Si 0.6 Mn 0.2 Fe Balance TABLE 2 Material Treatment Hardness (1) 4-6 brass 30% rolled, gold plated HV (2) 18-8 stainless steel Annealed 175 (3) AISI 430 (4) Pure iron 70 (5) Fe-Cr-Mo-Nb-alloy do The first experiment involved the ability of the various test watches to withstand the effects of a magnetic field. Watches with cases formed from each of the five types of materials were placed in a magnetic field, the intensity of which was varied. Variations in the rate of each of the watches was measured as the intensity of the field 'was increased. Preliminary experiments revealed that the greatest variation in the rate of watches placed in magnetic fields occurs when the magnetic lines of force are parallel to the plane of the plate of the watch and perpendicular to the escapement line (escapement wheelanchor-balance). Accordingly, all of the tests were conducted under this most unfavorable condition. The movements were of the same caliber and similar torques were maintained on the various mainsprings during the course of the experiment.

The results of the above described tests are shown in the drawing. Brass and 18Cr-8Ni stainless steel cases, of which most watch cases are now made proved inefiective as a protection against the influences of the magnetic field. Themovements in the brass and 18Cr-8Ni stainless steel cases were adversely effected even by magnetic fields of relatively weak intensity. This result was expected from the nature of these materials. On the other hand, the pure iron case proved able to provide complete protection even when the intensity of the magnetic field was raised to 300 oe. An adverse effect on the rate of the watches having cases formed from AISI 430 and Fe-Cr-Mo-Nb alloy when the intensity of the field reached about 50 oe. and 100 oe. respectively.

3 Another experiment was performed to determine the residual effect of exposure to a magnetic field. Watches having cases formed from the five above mentioned types of material were exposed to a field of 80 e. for one minute. One hour later, the rates of the various watches were measured. The results of this experiment are shown in Table 3.

TABLE 3 Material of case: Residual effect, sec/day (1) Brass -21 (2) 18Cr-8Ni stainless steel 20 (3) AISI 430 3 (4) Pure iron 0 (5) Fe-Cr-Mo-Nb alloy 0 In performing the foregoing experiment, all conditions such as mainspring torque and temperature were maintained constant, the only variable being the material of the cases. As shown in Table 3, exposure to the magnetic field resulted in a substantial adverse residual effect on the watches with the brass and 18Cr-8Ni stainless steel cases. On the other hand, no residual effect was noted in watches having cases of pure iron and Fe-Cr-Mo-Nb alloy. The validity of the foregoing experiment is demonstrated by Table 4 which shows the intensities of the magnetic fields to which a watch might be exposed in the normal course of use. The comparison of the experimental results described above and the intensity of the magnetic fields to which watches are most likely to be exposed, leads to the conclusion that Fe-Cr-Mo-Nb alloy is an effective practical magnetic shielding material.

TAB LE 4 Source of magnetic field (Japan): Intensity, oe. Earth magnetic field (Japan) Experiments were also conducted to determine the corrosion resistance of cases made from various materials. Neither the brass nor the pure iron where considered in this experiment in view of the poor antimagnetic qualities of the former and the low corrosion resistance of the latter. Cases formed from the three remaining materials were worn for one year. It was observed that the AISI 430 case was extremely corroded, particularly at the attaching portion of the back cover and the case body. Accordingly, a case formed of that material would not be practical. On the other hand, the corrosion resistance properties of cases formed from the Fe-Cr-Mo-Nb alloys and the 18Cr-8Ni stainless steel were very similar, neither material being corroded at all.

Further, the Fe-Cr-Mo-Nb alloy has sufiicient strength to serve as the case for a watch without requiring further.

surface treatment. Cases according to the invention are particularly adapted for use in Wristwatches where the size and the weight of the watch is an important factor in the appearance thereof.

It will thus be seen that the object set forth above and those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in the above construction without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description are shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense. It is also understood that the iron frequently used as shielding in antimagnetic watches. Watch cases according to the invention provide substantial advantages over the prior art since they are less complicated in structure, easier to manufacture and assemble and more pleasing in appearance due to their lighter weight and smaller size.

It will thus be seen that the object set forth above, and those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in the above constructions without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

What is claimed is:

1. A case for watches having high resistance to corrosion and high permeability to protect the movement of said watch in said case from an external magnetic field said case being formed of a ferritic alloy by weight consisting essentially of 19.2% chromium, 2.0% molybdenum, .31% niobium, .03% carbon, the balance being iron.

2. A case for watches as recited in claim I wherein in addition to the chromium, molybdenum, niobium and carbon, in the amounts specified, the case incorporates .6% silicon and 0.2% manganese, the balance being iron.

3. A case in accordance with claim 2 where titanium is substituted for niobium in the same quantitative amount.

References Cited UNITED STATES PATENTS 2,056,765 10/1936 Becket --126F 2,080,001 5/1937 Becket 75-126F 2,183,715 12/1939 Franks 75126F 2,905,577 9/1959 Harris 7512 6F 3,183,080 5/1965 Harpster 75-1261 HYLAND BIZOT, Primary Examiner US. Cl. X.R. 75126; 5888 

